The present invention relates to a method of resolving an ambiguity in the estimation of vertical velocity of a moving underwater or surface vehicle. Three acoustic pulses are successively transmitted. They are received by a series of detectors located on the vehicle. The time difference between correlated first and second received pulses is measured. The time different between correlated first and third received pulses is also measured. The phase shifts between the three transmitted pulses and three received pulses is measured. This information is used to determine the vertical velocity of the vehicle.
In U.S. Pat. No. 4,244,026, two acoustic pulses are transmitted. They are received by a series of detectors located on a moving underwater vehicle. Certain of these detectors correlate these received pulses. The time difference between the two received pulses is measured. The phase shifts between the two transmitted pulses and two received pulses is measured. This information is used in an attempt to measure the vertical velocity of such a vehicle. However, there is an ambiguity in the vertical velocity. This ambiguity is noted in the first full paragraph in column 10 of the '026 patent. The ambiguity is due to an inability to distinguish between the difference in phase shifts of the first and second received pulses, and that difference plus 360 degrees or a multiple of 360 degrees.
The present invention relates to a method of resolving the ambiguity in the estimation of a vertical velocity component of a moving vehicle, that is produced by the technique of U.S. Pat. No. 4,244,026.